Cracking criterion for high strength Al-Cu alloys fabricated by selective laser melting

Abstract Cracking is one of the most serious problems for the development of selective laser melting (SLM) of high strength aluminum alloys. The process parameters applied in the SLM process determine the cracking severity in these alloys. The purpose of this study is to understand the correlation between the process and the solidification cracking during SLM of Al-Cu alloys. A model based on the modified Rosenthal’s equation and Feurer’s criterion was developed to predict the critical scanning velocity for the crack initiation during SLM. The calculated result shows that the molten pool center is the most susceptible to the crack initiation in the conductive molten pool, and the susceptibility increases as the distance from the observed point to the molten pool center increases. The overlapping of the molten pool can remelt the previous track, and thus the crack initiating during the previous scanning may be eliminated after the remelting. Therefore, a small hatch spacing is beneficial for manufacturing the crack-free components. The cracking is mainly affected by the mushy zone length and the cooling rate during the process. Hence, the composition strongly affects the cracking. Not only the solidification temperature range but also other thermo-physical properties affect cracking. The model was verified by two different Al-Cu alloys. The cracking initiation and the crack length were observed and measured to evaluate the applicability of the model. The experimental data and the calculation results agree well. The model can be used for the process control as well as the alloy development for SLM of Al-Cu alloys.